Fix Style/IfUnlessModifier violation (#335)

[This commit](8e53d18 ) violated Style/IfUnlessModifier in RuboCop, so I ran rubocop -a to autocorrect it.

Author: willnet

lib/capistrano/tasks/systemd.rake

@@ -58,9 +58,7 @@ namespace :sidekiq do
         git_plugin.execute_systemd('enable', git_plugin.sidekiq_service_file_name(config_file))
       end
 
-      if fetch(:sidekiq_enable_lingering)
-        sudo :loginctl, 'enable-linger', fetch(:sidekiq_lingering_user)
-      end
+      sudo :loginctl, 'enable-linger', fetch(:sidekiq_lingering_user) if fetch(:sidekiq_enable_lingering)
     end
   end